import java.util.Scanner;
public class Demo2 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n =scanner.nextInt();
        System.out.println(fib(n));
    }
    public static int fib(int n) {
        if(n==1||n==2)
            return 1;
        int f1 = 1;
        int f2 = 1;
        int f3 = 0;
        for(int i = 3;i <= n;i++) {
            f3 = f1+f2;
            f1 = f2;
            f2 = f3;
        }
        return f3;
    }
}
